© Crown copyright Met Office The stratosphere and Seasonal to Decadal Prediction Adam Scaife, Sarah Ineson, Jeff Knight and Andrew Marshall January 2009

© Crown copyright Met Office Intraseasonal to Seasonal Early studies suggested an NAO/AO response to imposed stratospheric changes in GCMs Observations show downward propagation of wind anomalies from the upper stratosphere Some studies show additional predictability from the stratosphere on monthly to seasonal timescales

© Crown copyright Met Office Dynamical forecast Dynamical forecast + 70hPa stat fcast Christiansen 2005 Downward propagating winds Baldwin and Dunkerton 2001 See also: Kodera et al 1990, Boville 1984 Surface wind at 60N

© Crown copyright Met Office Winter 2005/6 Extreme stratospheric warming Downward propagation Surface cooling and extreme snowfall

© Crown copyright Met Office Winter 2005/6 ensembles  Tropospheric models (HadAM/HadGAM) 50/25 members HadISST as a boundary condition  Tropospheric Model + stratospheric perturbation 25 members HadISST as lower boundary condition Perturbed stratosphere from 1 st Jan Zonal wind at 50hPa Adam Scaife ControlPerturbed Observed Scaife and Knight, QJRMS, 2008

© Crown copyright Met Office Standard model Extended model 39.3km 84.1km  HadGEM2-A 15-member ensemble hindcasts (1 Dec – 30 Apr)  15 winters, Extended and Standard Models

© Crown copyright Met Office Predictability of stratospheric warmings Improved seasonal prediction of European winter cold spells: StandardExtended 0.6 | | | | | 0.1Peak easterly magnitude (fraction of observed) 12 | 89 | 612 | 1215 | 1013 | 5Maximum lead time for capture (days) Event Mean 26 Feb Dec Dec Feb 1984 Zonal wind (10hPa,60N) (Ext | Stand) Marshall and Scaife, submitted

© Crown copyright Met Office Atmospheric blocking Climate models and weather forecasts underestimate blocking frequency after >5 days Strat-trop model reproduces maximum blocking frequency in both Pacific and Atlantic sectors Is ultra-high horizontal resolution essential? Climate model blocking frequencies (D’Andrea et al. 1997, Tibaldi and Molteni 1990)

© Crown copyright Met Office Interannual to Decadal It is not only the ocean which contains a long memory. Stratospheric processes have a long memory too! For example the QBO has a period of 2-3 yrs and is predictable for 1-2 cycles. Key elements of interannual to decadal variability are strongly influenced by stratospheric processes. Some key recent examples…..

© Crown copyright Met Office Remote El Nino effects Model El Nino anomaly (50hPa geopotential height) Observations (Hamilton, 1993) Ineson and Scaife, Nature Geoscience, (2009)

© Crown copyright Met Office Remote El Nino Effects Zonal WindTemperature Ineson and Scaife, Nature Geoscience, (2009)

© Crown copyright Met Office Remote El Nino Effects Jan-Feb PMSLJan-Feb T2m Ineson and Scaife, Nature Geoscience, (2009)

© Crown copyright Met Office Remote El Nino effects 50hPa gph Standard PMSL Extended

© Crown copyright Met Office Quasi-Biennial Oscillation 50mb geopotential height anomalies (m): QBOE-QBOW composites Negative phase of the AO, as observed (statistically significant) AnalysisModel Marshall and Scaife (2009), submitted

© Crown copyright Met Office Quasi-Biennial Oscillation - surface Surface temperature anomalies (K): QBOE-QBOW composites Cooling over northern Europe, as observed AnalysisModel AO response captured in early stages of winter seasonal hindcasts Better representation of the QBO could lead to improved forecasts at seasonal-to-multiannual timescales Marshall and Scaife (2009), submitted

© Crown copyright Met Office Quasi-Biennial Oscillation in models QBOW: 1963/64, 1982/83, 1992/93 and 1998/99 QBOE: 1962/63, 1974/75, 1983/84, 1989/90, 1991/92, 1995/96 and 1997/98 Standard model drifts to easterly bias (c.f. Hamilton and Boer 2008) Extended model simulates realistic QBO (Scaife et al., 2000) => Interannual predictability for extratropics in winter QBO anomaly, 30hPa DECJANFEBMARAPR

© Crown copyright Met Office Decadal climate: Antarctica Ozone depletion led to increased Antarctic winds from the stratosphere to the surface. Observations and models agree on the impact: cooling over pole surrounded by warming Ozone recovery expected by ~2060 so this signal will reverse Potential for decadal prediction skill? Change per 30 yrs, Thompson and Solomon (2002)

© Crown copyright Met Office Decadal climate: NAO trends “Tropospheric models” do not easily capture the observed NAO trend. Note 1960s to 1990s change

© Crown copyright Met Office Decadal NAO trends Change in NAO index Observations have a large increase in NAO Control run has very little increase in NAO (includes GHG, aerosols, observed SST etc) NAO U 50hPa Both NAO and stratospheric wind increase Decrease in recent years Similar multiannual variability

© Crown copyright Met Office Decadal NAO trends Change in NAO indexChange in surface pressure Impose a body force in the model stratosphere (c.f. Norton 2003) => Increase in stratospheric wind from 1960s to 1990s => Increase in NAO similar to observed value

© Crown copyright Met Office Decadal Surface Climate trends Model TemperatureObserved Temperature European T trends 1960s-1990s HadAM3 ctl 0.15K/decade HadAM3 expt 0.59K/decade Observations 0.53K/decade Model PrecipitationObserved Precipitation Scaife et al. GRL, 2005

© Crown copyright Met Office Stratospheric dynamics are important for seasonal to decadal surface variability Several sources of predictability/variability: Sudden Warmings -> persistent anomalies 30-60d ENSO -> extratropics -> stratosphere -> NAO Volcanoes -> stratosphere -> extratropics -> NAO QBO -> extratropics -> NAO Decadal climate variability involves the stratosphere Low lid models do not represent these processes Necessary to achieve good skill for the extratropics

© Crown copyright Met Office SPARC – Stratospheric Processes And their role in Climate 1 - Climate-Chemistry Interactions How will stratospheric ozone and other constituents evolve? How will changes in stratospheric composition affect climate? What are the links between changes in stratospheric ozone, UV radiation and tropospheric chemistry? 2 - Detection, Attribution, and Prediction of Stratospheric Change What are the past changes and variations in the stratosphere? o How well can we explain past changes in terms of natural and anthropogenic effects? How do we expect the stratosphere to evolve in the future, and what confidence do we have in those predictions? 3 - Stratosphere-Troposphere Dynamical Coupling What is the role of dynamical and radiative coupling with the stratosphere in extended-range tropospheric weather forecasting and determining long-term trends in tropospheric climate? By what mechanisms do the stratosphere and troposphere act as a coupled system?

© Crown copyright Met Office SPARC Activities Gravity Waves Data Assimilation CCM Validation Laboratory Studies joint with IGAC SOLAR Influence for SPARC (SOLARIS) SPARC Dynamical Variability Activity DynVar Top DynVar intraseasonal DynVar climate change DynVar ideal ALL LONG SIMULATIONS – not initialised UTLS/SPARC Tropopause Initiative

© Crown copyright Met Office Possible WGSIP/SPARC interaction and stratospheric experiments Hi Top – Low Top Hindcasts? Parallel to WGSIP-CHFP Extended models Same initial ocean data? Just initialising extra atmosphere? Interannual predictability from the QBO? Extended model or a simple parametrization (available) Easy experiment – cheap. Requires a few years of E and W QBO with a reasonable number of members. Could lead directly to forecast improvements.